314 



KELVIN 



would yield to and from the moon, and the water would 

 not move at all relatively to the crust. If the earth were 

 even as rigid as glass all through, calculation shows that the 

 solid would yield so much that the tides could only be about 

 one third of what they would be if the earth were perfectly 

 rigid. Again, if the earth were two or three times as rigid 

 as glass, about as rigid as a solid globe of steel, it would 



FIG. 134 Elastic Tides 



still, considering its great dimensions, yield two or three 

 feet to that great force, which elastic yielding would be 

 enough to make the tides only two thirds of what they 

 would be if the earth were perfectly rigid. Mr. G. Darwin 

 has made the investigation by means of the lunar fortnightly 

 tides, and the general conclusion, subject to verification, is 

 that the earth does seem to yield somewhat, and may havf 

 something like the rigidity of a solid globe of steel. 



